High Throughput Current-Voltage Combinatorial Characterization Tool and Method for Combinatorial Solar Test Substrates

ABSTRACT

Measuring current-voltage (I-V) characteristics of a solar cell using a lamp that emits light, a substrate that includes a plurality of solar cells, a positive electrode attached to the solar cells, and a negative electrode peripherally deposited around each of the solar cells and connected to a common ground, an articulation platform coupled to the substrate, a multi-probe switching matrix or a Z-stage device, a programmable switch box coupled to the multi-probe switching matrix or Z-stage device and selectively articulating the probes by raising the probes until in contact with at least one of the positive electrode and the negative electrode and lowering the probes until contact is lost with at least one of the positive electrode and the negative electrode, a source meter coupled to the programmable switch box and measuring the I-V characteristics of the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/334,165, filed May 12, 2010 and entitled “High ThroughputCombinatorial Characterization Tool for Combinatorial Solar TestSubstrates,” the contents of which, in its entirety, is hereinincorporated by reference.

BACKGROUND

1. Technical Field

The embodiments herein generally relate to solar processing andcharacterization, and more specifically, to a high throughputcombinatorial characterization tool for combinatorial solar testsubstrates.

2. Description of the Related Art

Some exemplary solar processing operations include operations for adding(depositions) and removing layers (etch), defining features, preparinglayers (e.g., cleans), doping, etc. However, solar companies conductresearch and development (R&D) on full substrate processing, often onvery large substrates and requiring a complete solar cell manufacturingline. This approach has resulted in high R&D costs and the inability toconduct extensive experimentation in a timely and cost effective manner.Combinatorial processing as applied to solar manufacturing operationsenables multiple experiments to be performed on a single substrate andwithout a complete solar cell manufacturing line. Equipment forperforming the combinatorial processing and characterization of thecombinatorial test substrates must support the efficiency offeredthrough the combinatorial processing operations.

Combinatorial processing enables rapid evaluation of solar processingoperations. The systems supporting the combinatorial processing areflexible to accommodate the demands for running the different processeseither in parallel, serial, or some combination of the two. A valuablecomponent of the systems for combinatorial processing are thecharacterization tools used to produce the data from high throughputexperimentation in such a way that the process does not slow down. Highperformance combinatorial characterization tools are needed to quicklyprocess and characterize the combinatorial test substrates.

Conventional solar electrical characterizations, such as current vs.voltage measurements in an R&D environment, are performed independentlyof one another in a manual and sequential mode. However, theconventional process tends to be time consuming and resource demandingresulting in a significant loss in testing throughput. For example, whenthere is a need for measuring multiple sites per sample, the throughputand resources of the operators becomes a critical issue. Taking 32 sitesper sample as an example, it takes several minutes to measure thecurrent vs. voltage performance per site. To finish the characterizationof each example, the operator has to move the sites every few minutesuntil every site on the sample has been tested. It is a lengthy andtiring test.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1 illustrates a schematic diagram of a combinatorial screeningprocess according to an embodiment herein;

FIG. 2 illustrates a block diagram of a multi-pin combinatorialcharacterization apparatus according to an embodiment herein;

FIG. 3A illustrates a schematic cross-sectional diagram of acombinatorial test sample according to an embodiment herein;

FIG. 3B illustrates a schematic top view diagram of a combinatorial testsample according to an embodiment herein;

FIG. 4A illustrates a block diagram of a Z-stage combinatorialcharacterization apparatus according to an embodiment herein;

FIG. 4B illustrates a block diagram of a Z-stage combinatorialcharacterization apparatus in transition according to an embodimentherein;

FIG. 5A illustrates a schematic diagram of a current-voltage measurementtool according to an embodiment herein;

FIG. 5B illustrates a schematic diagram of the rotation of anarticulation platform of a current-voltage measurement tool according toan embodiment herein;

FIG. 6A illustrates a schematic diagram of an unloaded sample trayaccording to an embodiment herein;

FIG. 6B illustrates a schematic diagram of a loaded sample trayaccording to an embodiment herein;

FIG. 7 illustrates a block diagram of a multi-axis control deviceaccording to an embodiment herein;

FIG. 8 illustrates a flowchart of a method according to an embodimentherein; and

FIG. 9 illustrates a computing system according to an embodiment herein.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

With increasing energy demands, alternative (e.g., green) energy gainsmore and more attention. As an important part of the research anddevelopment of solar cells, the electrical characterization of thosesolar cells also needs to improve. Measurement of the current-voltage(I-V) efficiency of a solar cell is a valuable parameter to judge thecell performance. It determines how efficiently the solar energy can beconverted into electricity. For example, efficiency may be characterizedby measuring the current-voltage curve of the cell under standard onesun illumination. According to several embodiments herein, a solarsimulator is used as the light source with less than 1% spectrumdifference as actual sunshine. The current generated by an illuminatedsolar cell is measured as the voltage scan by connecting the electrodesof the cell to a source meter.

The embodiments herein provide a high performance combinatorialcharacterization tool that saves both operator resources as well as testtime, and offers a key function for high throughput and combinatorialresearch. Referring now to the drawings, and more particularly to FIGS.1 through 9, where similar reference characters denote correspondingfeatures consistently throughout the figures, there are shown severalembodiments.

Combinatorial processing systems are only as good as thecharacterization available. Therefore, the high performancecharacterization tool described herein provides the means by which truehigh throughput experimentation may be accomplished. The operator burdencan be minimized by test automation. The test time can be significantlyreduced by parallel testing by measuring multiple sites at the same timeinstead of measuring one at a time. Although the high performancecharacterization tool described herein exhibits extraordinary utility inthe field of combinatorial processing (e.g., by enabling high throughputexperimentation), the embodiments herein, however, are not limited tocombinatorial processing. Thus, the use of the high performancecharacterization tool described herein in combinatorial processingsystems represents one of many valuable applications of the embodimentsherein. For example, traditional solar cell experimentation andexploration methods, semiconductor manufacturing and fabrication, lightemitting diode (LED) applications, flat panel display applications,characterization of photochromic materials, characterization ofelectrochromic materials, and characterization of thermochromicmaterials, among other applications, would all benefit from the highthroughput and rapid characterization offered by the high performancecharacterization tool described herein.

As described above, during one embodiment of combinatorial processing,each wafer is subjected to many different process conditions. FIG. 1illustrates an example of such a combinatorial screening process. Asshown in FIG. 1, combinatorial screening process 100 includes primaryscreening process (110), secondary screening process (120), and tertiaryscreening process (130). In FIG. 1, for example, numerous materialscompositions (e.g., 18 spots or 46 spots on a single wafer, where eachspot is a unique material composition) are systematically explored on asingle wafer during an initial primary screening process (110) at speedsthat would otherwise be impossible using traditional methods and tools.In other words, in the embodiment shown in FIG. 1, primary screeningprocess (110) is an initial screening that processes many samples torule out materials for further screening. Once the best materials,process conditions, or process integration are identified using initialcombinatorial screening methods (e.g., during primary screening process(110)), that material is then scaled up to test the performance (e.g.,current-voltage performance) of that material and/or conditions during asecondary screening stage (e.g., secondary screening process (120)).Furthermore, according to one embodiment herein, additional testing maytake place during the tertiary screening process (130). During thetertiary screening process (130), for example, the materials and/orprocess conditions that were not filtered out during the primaryscreening process (110) and the secondary screening process (120) arescaled up to a full-scale device size. Furthermore, due to the speed andnon-destructiveness of the performance test (described in further detailbelow) occurring in the secondary screening process (120), materialand/or conditions that pass both the primary screening process (110) andthe secondary screening process (120) can rapidly proceed to thetertiary screening process (130). Consequently, to test the performanceof these material compositions, embodiments herein utilize an improvedmeasurement tool to enable the collection of information more rapidly.

FIG. 2, with reference to FIGS. 1, 3B, 6A, 6B, 7, and 9, illustrates ablock diagram of a multi-pin combinatorial characterization apparatus 1according to an embodiment herein. As shown in FIG. 2, multi-pincombinatorial characterization apparatus 1 includes a lamp 10, light 15(emitted from lamp 10), substrate 40, probes 45, switching matrix 50,programmable switch box 55, and source meter 60. The lamp 10 maycomprise a solar simulator and the light 15 may comprise natural lightwith less than 1% difference of sunlight. As described in further detailbelow, substrate 40, according to one embodiment, includes glass 20, atransparent conducting oxide (TCO) coating 25, electrodes 30 a, 30 b,and a solar cell 35. Also shown in the embodiment of FIG. 2, theelectrodes (e.g., electrodes 30 a, 30 b) are transferred to a backsurface (e.g., TCO 25) of substrate 40 where substrate 40 is not exposedto light (e.g., light 15 emitted from lamp 10) in a configurationsuitable for backside probing. While not shown in FIG. 2, those ofordinary skill in the art could reverse the configuration shown in FIG.2 to enable frontside probing as well. In the embodiment shown in FIG.2, each solar cell 35 of substrate 40 can be processed under varied wet(e.g. texturing) or dry (electrode sputtering, absorber layerdeposition) conditions during the combinatorial processing (e.g.,primary screening process (110), shown in FIG. 1). In the embodimentshown in FIG. 2 and further illustrated in FIGS. 3A and 3B, the areainside of solar cell 35 includes a positive electrode 30 a while thearea outside of the solar cell 35 is connected to a common electricalground (e.g., electrode 30 b). According to one embodiment herein,electrodes 30 a, 30 b are formed by chemical vapor deposition (CVD) andisolated by a light scribing process on substrate 40. As discussed infurther detail below, light 15 generated from lamp 10 is usedindividually to test the performance of solar cells 35, and in oneparticular embodiment, the solar cells 35 may be individualsite-isolated devices on a combinatorial solar test substrate 40 whereeach of the site-isolated devices has been varied as compared to oneanother. In alternate embodiments, the substrate 40 being tested may bea substrate 40 having multiple unvaried solar cells 35 produced foreither commercial or research and development purposes. Examples of asolar test substrate 40 include, but are not limited to: copper indiumgallium diselenide (CIGS), copper zinc tin sulfide (CZTS), and otherthin film photovoltaic (TFPV) materials with a silicon or glasssubstrate.

In addition, as shown in FIG. 2, electrodes 30 a, 30 b are connected toa selective circuit (e.g., switching matrix 50). In one embodimentherein, a connection between electrodes 30 a and 30 b is made throughswitching matrix 50, which is designed to match the geometry ofsubstrate 40 with at least one probe 45 touching the inside of eachsolar cell 35 (e.g., electrode 30 a) and the other probe 45 touching thenearby outside of each solar cell 35 (e.g., electrode 30 b). Forexample, switching matrix 50 may include a plurality of probes 45, whereeach probe 45 includes a spring-loaded pin (e.g., pins 163, shown inFIG. 7) used for better contact and reduced series resistance. Inaddition, substrate 40 may be seated on a substrate support structure 50a and held in place by vacuum or by mechanical means, such as a clamp,or a combination of both (e.g., as further described with respect toFIGS. 6A and 6B). With a measurement device (e.g., source meter 60)operatively connected to a selective circuit (e.g., as defined by thecontacts made by electrode 30 a and 30 b on substrate 40), a controlprogram (e.g., as stored and executed by a computing system 200, asshown in FIG. 9) automatically selects one site (e.g., solar cell 35) onsubstrate 40 for testing and may continue in series with the next site(e.g., solar cell 35) until all of the sites on substrate 40 are tested.

FIG. 3A, with reference to FIGS. 1 and 2, illustrates a schematiccross-sectional diagram of a combinatorial test sample (e.g., substrate40) according to an embodiment herein. Moreover, FIG. 3B, with referenceto FIGS. 1 through 3A, illustrates a schematic top view diagram of acombinatorial test sample (e.g., substrate 40) according to anembodiment herein. As discussed above and shown in FIGS. 3A and 3B,substrate 40 includes glass 20, a transparent conducting oxide (TCO)coating 25, electrodes 30 a, 30 b, and a solar cell 35. In addition,each solar cell 35 of substrate 40 is combinatorially varied. Forexample, in one embodiment, the combinatorial variation of the solarcells 35 includes varied texturing by wet chemistry or varied thin filmdeposition by dry process tools. Moreover, for each solar cell 35,electrode 30 a includes a metal electrode attached to the area insidesolar cell 35 that has the individual separated electrode (e.g.,electrode 30 a) connecting to the current-voltage source during test.Furthermore, for each solar cell 35, electrode 30 b includes a metalarea outside of solar cell 35 connected to a common electrode (e.g.,electrode 30 b) that is further connected to ground.

FIG. 4A, with reference to FIGS. 1 through 3B and 9, illustrates a blockdiagram of a Z-stage combinatorial characterization apparatus 5according to an embodiment herein. The embodiments, as described herein,utilize the X, Y, and Z axes to define various geometric planesassociated with the components described herein. Those skilled in theart would recognize that the X, Y, and Z axes may be configured in anysuitable orientation, and the embodiments herein are not restricted toany particular orientation. As shown in FIG. 4A, Z-stage combinatorialcharacterization apparatus 5 includes a lamp 10, light 15 (emitted fromlamp 10), substrate 40, probes 45, Z-stage device 70 and source meter60. Z-stage combinatorial characterization apparatus 5 also includes amulti-axis (e.g., X-Y) stage tray 50 b. The X-Y stage tray 50 b may becooled by air around the X-Y stage tray 50 b.

As described above, substrate 40, according to one embodiment, includesat least one solar cell 35, where solar cell 35 includes glass 20, atransparent conducting oxide (TCO) coating 25, and electrodes 30 a, 30b. Also shown in the embodiment of FIG. 4A, all of the electrodes (e.g.,electrodes 30 a, 30 b) are transferred to a back surface (e.g., TCO 25)of substrate 40 where substrate 40 is not exposed to light (e.g., light15 emitted from lamp 10) in a configuration suitable for backsideprobing. Again, those of ordinary skill in the art could reverse theconfiguration shown in FIG. 2 to enable frontside probing. In theembodiment shown in FIG. 4A, each solar cell 35 of substrate 40 can beprocessed under varied wet (e.g. texturing) or dry (electrodesputtering, absorb layer deposition) conditions during the combinatorialprocessing (e.g., primary screening process (110), shown in FIG. 1).

In the embodiment shown in FIG. 4A and further illustrated above in FIG.3B, the area inside of solar cell 35 attaches to a positive electrode 30a while the area outside of the solar cell 35 is the common electricalground (e.g., electrode 30 b). According to one embodiment herein,electrodes 30 a, 30 b are formed by chemical vapor deposition (CVD) andisolated by a light scribing process on substrate 40.

In addition, as shown in FIG. 4A, electrodes 30 a, 30 b are operativelyconnected to a selective circuit (e.g., Z-stage device 70). In oneembodiment herein, a connection between electrodes 30 a and 30 b is madethrough Z-stage device 70, which includes a plurality of probes 45(e.g., two probes 45 is shown in FIG. 4A) where at least one probe 45touches the area inside of each solar cell 35 (e.g., electrode 30 a) andanother probe 45 touches the nearby outside area of each solar cell 35(e.g., electrode 30 b). In addition, as described in further detailbelow, X-Y stage tray 50 b and substrate 40 can be held together byvacuum or by mechanical means, such as a clamp, or a combination ofboth. With a measurement device (e.g., source meter 60) operativelyconnected to a selective circuit (e.g., as defined by the contacts madeby electrode 30 a and 30 b on substrate 40), a control program (e.g., asstored and executed by computing device 200 shown in FIG. 9)automatically selects one site (e.g., solar cell 35) on substrate 40 fortesting and may continue in series with the next site (i.e., solar cell35) until all of the sites on substrate 40 are tested.

In FIG. 4A, instead of the geometry-matched switching matrix 50 ofmulti-pin combinatorial characterization apparatus 1 shown in FIG. 2,only two probes 45 attached to Z-stage device 70 are used with one probe45 touching the area inside of the solar cell 35 and the other probe 45contacting the area outside of the solar cell 35. Substrate 40 is alsomounted on X-Y stage tray 50 b for movement along an X-Y plane (incontrast to the stationary substrate support structure 50 a of multi-pincombinatorial characterization apparatus 1 shown in FIG. 2) and probes45 are fixed onto Z-stage device 70 to provide movement along a Z-plane.After finishing testing a solar cell 35, Z-stage device 70 lowers probes45 to disconnect probes from electrodes 30 a, 30 b. Substrate 40 is thenmoved to the next site (as described below) using X-Y stage tray 50 band the connection to electrodes 30 a, 30 b is restored (as shown in thesequential diagram in FIG. 4B).

The multi-pin combinatorial characterization apparatus 1 shown in FIG. 2may be used for parallel testing. The Z-stage combinatorialcharacterization apparatus 5 shown in FIG. 4A also has good site-to-siterepeatability because the light (e.g., lamp 10) is fixed. Theseembodiments may also be universal for any kind of test substrate and nospecific fixture is required, particularly for Z-stage combinatorialcharacterization apparatus 5 shown in FIG. 4A. Besides the automation,multi-pin combinatorial characterization apparatus 1 can alsosignificantly increase throughput by enabling parallel testing.According to embodiments herein, I-V testing can be automated and thesite-isolated regions of a test substrate may be tested in parallel.Consequently, the embodiments herein increase throughput oncharacterization significantly over the conventional techniques where anoperator is manually required to measure each sample. In addition, inone embodiment of multi-pin combinatorial characterization apparatus 1,a multi-channel source meter 60 is coupled to switching matrix 50, wherean individual measurement channel is assigned for each solar cell 35 onsubstrate 40 in order to achieve further throughput gains throughparallelism.

In addition, a characterization tool based on multi-pin combinatorialcharacterization apparatus 1 or Z-stage combinatorial characterizationapparatus 5 can optionally measure the temperature of the solar cell 35currently being measured and correct for any temperature increase thatoccurs (e.g., due to expose of light 15 from lamp 10) of substrate 40.Alternatively, substrate 40 may be cooled during the characterization ofthe solar cell 35 to maintain a steady temperature during eachmeasurement. For example, in one embodiment, a heat sink (not shown) isused to cool substrate 40. In yet another alternate embodiment,substrate 40 can be pre-heated to a temperature sufficient to mitigateany ancillary heating, caused by the lamp 10 used during the I-Vmeasurement.

FIG. 5A, with reference to FIGS. 1 through 4B, illustrates a schematicdiagram of an I-V measurement tool 90 according to an embodiment herein.As shown in FIG. 2, I-V measurement tool 90 includes a full spectrumlamp 10, shutter 92, substrate 40, sample tray 80, support platform 94,and articulation platform 96. Also shown in FIG. 5A is light 15 emittedfrom full spectrum lamp 10. In the embodiment shown in FIG. 5A, sampletray 80 is located at a fixed distance (e.g., approximately 2-5 inches)from shutter 92. As described in further detail below, one embodiment ofarticulation platform 96 includes an X-Y stage tray 50 b to move sampletray 80 along two axes to enable full coverage of substrate 40 whilemaintaining a fixed distance from shutter 92. In the embodiment shown inFIG. 5A, I-V measurement tool 90 further includes Z-stage device 70 onarticulation platform 96 and under sample tray 80 to move probes 45(shown in FIG. 4A) along a vertical plane.

I-V measurement tool 90 may further include a transmittance detector 97(along with Z-stage device 70) on articulation platform 96 and undersample tray 80 to measure the transmittance of a thin film glass solarcell 35 on substrate 40 or the I-V efficiency of an electrochromicmaterial in another potential use of this tool where multipleelectrochromic materials are deposited and varied from one another onsubstrate 40. In such an embodiment, articulation platform 96 rotates(e.g., as shown in FIG. 5B) to align the transmittance detector 97 undersolar cell 35 on substrate 40 and shutter 92. Transmittance is useful,for example, when developing electrochromic materials and thereforethere is a need to shine light 15 through the substrate 40 to measurethe transmittance of the electrochromic material.

FIG. 6A, with reference to FIGS. 1 through 5B, illustrates a schematicdiagram of an unloaded sample tray 80 according to an embodiment herein.In addition, FIG. 6B, with reference to FIGS. 1 through 6A, illustratesa schematic diagram of a loaded sample tray 80 according to anembodiment herein. As shown in the embodiment of FIGS. 6A and 6B, sampletray 80 includes a support frame 82 to hold substrate 40, wheresubstrate 40 may include one solar cell 35 or multiple solar cells 35.According to one embodiment herein, when there are multiple solar cells35 on substrate 40, each solar cell 35 is combinatorially varied.Substrate 40 is held in place by clamp 84, where clamp 84 is secured viachannels 86. The channels 86 may be configured as a lip/ledge on whichthe substrate 40 rests, or the channels 86 may include vacuum-likeproperties to further retain the substrate 40 thereon. Operativelyconnected to support frame 82 are sample guides 88 a, 88 b, which areperpendicularly coupled to each other. In addition, while not shown inFIGS. 6A and 6B, in one embodiment, the sample tray 80 may betemperature controlled to regulate the temperature of the substrate 40being tested. Substrate 40 is secured to the support frame 82 bypositioning the substrate 40 at a corner 85 of the channels 86. Thesample guide 88 a moves axially and translationally with respect tosample guide 88 b and the support frame 82 to accommodate differentsizes of substrate 40. Once positioned on the sample guide 88 a andaligned in the channel 86, the substrate 40 is locked in place with theclamp 84, which, in one embodiment, may use a vacuum (not shown) tofurther retain the substrate 40 in place.

FIG. 7, with reference to FIGS. 1 through 6B and 9, illustrates a blockdiagram of a multi-axis (e.g., X-Y) control device according to anembodiment herein. As shown in FIG. 7, multi-axis control device 150includes an X-axis articulator 152 (e.g., a step motor), a Y-axisarticulator 154 (e.g., a step motor), an X-axis controller 156 (e.g.,SMC100CC controller, manufactured by Newport Corporation, Irvine,Calif., USA), an optional remote controller 156 a, a Y-axis controller158 (e.g., SMC100CC controller, manufactured by Newport Corporation,Irvine, Calif., USA), an optional remote controller 158 a, a powersupply 160, a pneumatic solenoid 162, and a DC power supply 164.According to one embodiment herein, remote controllers 156 a and 158 aare operatively coupled to remote server 157 (e.g., computing device 200shown in FIG. 9) to allow remote control and automation of X-axiscontroller 156 and Y-axis controller 158, respectively. In addition,according to one embodiment herein, pneumatic solenoid 162 is coupled toa plurality of connectors (e.g., pins 163 or probes 45), whicharticulate (via pneumatic solenoid 162) to form connections to substrate40 on articulation platform 96. The pins 163, as shown in FIG. 7, may beconfigured as push-pins that include a spring at the tip to pressagainst the electrodes of the substrate 40, or they may be sharp tippedstiff pins, or any other type of suitable probe. As shown in FIG. 7,pneumatic solenoid 162 as well as X-axis controller 156 and Y-axiscontroller 158 are coupled to power supplies (i.e., power supply 160 andpower supply 164, respectively). While shown in FIG. 7 as two separatepower supplies, (e.g., power supply 160 and power supply 164), theembodiments herein are not limited to such a configuration and those ofordinary skill in the art could easily consolidate power supply 160 andpower supply 164 into a single power supply connected to pneumaticsolenoid 162 as well as X-axis controller 156 and Y-axis controller 158.

Moreover, according to one embodiment herein, multi-axis control device150 is operatively coupled to articulation platform 96 (shown in FIG.5A, which may include X-Y stage tray 50 b shown in FIG. 4A) and sampletray 80 to move sample tray 80 (shown in FIGS. 5 through 6B) along anX-axis and/or along a Y-axis. In so doing, multi-axis control device 150moves substrate 40 (shown in FIG. 2) along a plane that is located at afixed distance from shutter 92 (shown in FIG. 5A) to vertically alignspecially treated portions (e.g., solar cell 35) of substrate 40 withshutter 92. In another embodiment, the articulation platform 96 isactively cooled by air around the articulation platform 96.

The specially treated portions of substrate 40 may include portions(e.g., solar cell 35) prepared using combinatorial processing. Forexample, combinatorial processing provides rapid evaluation of solarprocessing operations. Some exemplary solar processing operationsinclude operations for adding (depositions) and removing layers(etching), defining features, preparing layers (e.g., cleans), doping,etc. In such an embodiment, the systems supporting the combinatorialprocessing are flexible to accommodate the demands for running thedifferent processes either in parallel, serial, or some combination ofthe two. It is to be understood that the embodiments herein are notlimited to the combinatorial development and testing of solar cells 35,but may also be used to test electrochromic materials, photochromicmaterials, thermochromic materials, etc.

As used herein, combinatorial processing may include any processing(e.g., solar processing) that varies the processing conditions in two ormore regions of a substrate 40. A substrate 40 may be, for example, asilicon substrate 40 such as a wafer that is used in solar processing. Aregion of a substrate 40 may be any portion of the substrate 40 that issomehow defined, for example by dividing the substrate 40 into regionshaving predetermined dimensions or by using physical barriers, such assleeves, over the substrate 40. The region may or may not be isolatedfrom other regions. For example, a substrate 40 may be divided into twoor more regions, each of which may or may not include solar cellstructures 35 (e.g., Cu₂ZnSnS₄ solar cell structures and copper indiumgallium diselenide solar cell structures may occupy separate regions).

A process may be performed at each of the regions. For example, a firstregion is cleaned using a first cleaning agent, and a second region iscleaned using a second cleaning agent. The efficacies of the twocleaning agents are evaluated, and none, one, or both of the cleaningagents may be selected as suitable candidates for larger scaleprocessing (e.g., on regions with structures, or regions enabling moresophisticated testing, or a full substrate, etc.). According to otherexamples, multiple iterations of the same experiment are performed onthe same substrate 40, and any number of regions may be defined. Forexample, five cleaning solutions may be tested using fifteen regions ofa substrate 40, each cleaning solution being tested three times.

FIG. 8, with reference to FIGS. 1 through 7 and 9, illustrates a flowdiagram according to an embodiment herein. Step (170) of the method ofFIG. 8 includes receiving a combinatorially varied test substrate (e.g.,substrate 40 shown in FIG. 1). Step (172) includes determining whetherto use a frontside or backside probing device (e.g., thin film solarcells and LED's would use backside probing device, such as Z-stagecombinatorial characterization apparatus 5 shown in FIG. 4A and CIGS orCZTS solar cells would use frontside probing device (not shown)). Step(174) includes determining a number of probes (e.g., probes 45) neededto test a test substrate cell (e.g., solar cell 35 shown in FIG. 3B).Furthermore, step (176) includes programming a measurement tool (e.g.,Z-stage combinatorial characterization apparatus 5 shown in FIG. 4A),which includes the locations (e.g., coordinates of the multiple processconditions within the site-isolated regions (e.g., solar cell 35) of thetest substrate (e.g., substrate 40) and the thickness of each processcondition at the site-isolated regions (e.g., solar cell 35) to achievegood contact between the probes 45 and the electrodes (e.g., electrodes30 a, 30 b). Step (178) of the method shown in FIG. 8 characterizes theprocess conditions within each of site-isolated region (e.g., solar cell35) using an I-V measurement device (e.g., Z-stage combinatorialcharacterization apparatus 5 shown in FIG. 4A).

A representative hardware environment for practicing the embodimentsherein is depicted in FIG. 9, with reference to FIGS. 1 through 8. Thisschematic drawing illustrates a hardware configuration of an informationhandling/computer system 200 (e.g., for programming a measurement toolas described in step (176) of FIG. 8) in accordance with the embodimentsherein. The system 200 comprises at least one processor or centralprocessing unit (CPU) 210. The CPUs 210 are interconnected via systembus 212 to various devices such as a random access memory (RAM) 214,read-only memory (ROM) 216, and an input/output (I/O) adapter 218. TheI/O adapter 218 can connect to peripheral devices, such as disk units211 and tape drives 213, or other program storage devices that arereadable by the system 200. The system 200 can read the inventiveinstructions on the program storage devices and follow theseinstructions to execute the methodology of the embodiments herein. Thesystem 200 further includes a user interface adapter 219 that connects akeyboard 215, mouse 217, speaker 224, microphone 222, and/or other userinterface devices such as a touch screen device (not shown) to the bus212 to gather user input. Additionally, a communication adapter 220connects the bus 212 to a data processing network 225, and a displayadapter 221 connects the bus 212 to a display device 223 which may beembodied as an output device such as a monitor, printer, or transmitter,for example.

Embodiments herein provide a measurement tool (e.g., I-V measurementtool 90) that permits a sample (e.g., as prepared using combinatorialprocesses on substrate 40) to be loaded once and all other testingfunctions association with current-voltage measurements to be automated.In addition, such automation provides greater efficiency (e.g., lesstime to conduct the measurements because both the current-voltagemeasurements are performed without human intervention) over conventionalsystems. Embodiments herein also provide greater throughput (e.g.,performing multiple measurements in parallel) and greater accuracy(e.g., programmable control of a sample).

The embodiments herein provide a measurement tool (e.g., I-V measurementtool 90) that permits a sample (e.g., as prepared using combinatorialprocesses) to be loaded once and all other testing functions inassociation with current-voltage measurement to be automated. Inaddition, such automation provides greater efficiency (e.g., less timeto conduct the measurements) over conventional systems, which would beadvantageous for any research and development but may be of particularvalue in improving the throughput for combinatorial testing. The speedat which the solar cells 35 are characterized is valuable in achievinghigh performance combinatorial processing. Embodiments herein alsoprovide greater precision and greater accuracy of the measurements.

One embodiment of the combinatorial screening process described above(e.g., FIG. 1) enables multiple experiments to be performed on a singlesubstrate 40 and the rapid evaluation of solar cell processingoperations and solar cell materials. Multiple solar cells 35 may resideon a single substrate 40 and are designed to run the differentcombinatorial processes either in parallel, serial, or some combinationof the two. For example, embodiments herein allow forming differenttypes of thin film solar cells, CZTS solar cells, CIGS solar cells, andcadmium telluride (CdTe) solar cells that can be combinatorially variedand evaluated. These methodologies all incorporate the formation ofsite-isolated regions using a combinatorial processing tool and the useof these site-isolated regions to form the solar cell area. Therefore,multiple solar cells 35 may be rapidly formed on a single substrate 40for use in combinatorial methodologies. Any of the individual processesof the methods described herein may be varied combinatorially to testvaried process conditions or materials.

The use of combinatorial-based rapid device prototyping methods (e.g.,as shown in FIG. 1) permits fabrication, comprehensive characterization,and analysis of hundreds of unique solar cells 35 on a weekly basis todramatically increase learning rates. Alternative device structures,process integration schemes, and material compositions aresystematically explored at speeds that would otherwise be impossibleusing traditional methods and tools. This pace of development applied toEarth-abundant TFPV devices may represent an order of magnitudeacceleration of R&D in this area.

For example, CZTS is a compound semiconductor that evolves from thechalcopyrite structured I-III-VI2 compound CIGS, where indium/gallium issubstituted by zinc/tin and selenium by sulfur. The substituted elementsin CZTS are comparatively orders of magnitude more abundant than CIGSelements. CZTS has a band gap between approximately 1.45 and 1.6 eV,which is very close to the optimum value of an absorber layer of a solarcell 35. Additionally, the band edge absorption coefficient of CZTS isabove 1×10⁴ cm⁻¹ which enables its use as a thin film solar cellabsorber candidate.

A standard CZTS device structure may include the deposition of fourprimary layers on a substrate: a back contact (e.g., Mo), an absorberlayer (e.g., CZTS), a buffer layer (e.g., CdS or ZnS), and a frontcontact (e.g., ITO or Al:ZnO). Each material and deposition processprovides an opportunity to reduce manufacturing costs and increase cellefficiencies by using the combinatorial process described herein.Moreover, the similarity in process flow relative to current CIGSprocesses offers the intriguing possibility of retrofitting legacyproduction assets to produce lower cost devices using moreenvironmentally friendly, Earth-abundant materials.

Various techniques can be used for depositing the CZTS absorber layer,which is the most critical layer in the device stack. These techniquesinclude electron beam deposition continued by sulfurization, hybridsputtering, vacuum evaporation with sulfurization, sol-gel followed byH₂Se annealing, pulsed laser deposition, sputtering followed bysulfurization, single step RF sputtering, electroplating, and spraypyrolysis.

As described above, the embodiments herein improve the combinatorialscreening and the characterization of compounds (e.g., CIGS absorptionlayers, CZTS absorption layers, and other chalcopyrite structuredI-III-VI2 compound CIGS absorption layers) after the application ofthose formulations. For example, during an initial screening (e.g.,primary screening process ((110)) shown in FIG. 1), many samples (e.g.,18 spots or 46 spots on a single wafer, where each spot is a uniquematerial composition) are created using blanket films (e.g., as suppliedby Advantiv Technologies, Inc. Fremont Calif., USA) and thereaftertested. This initial screening (e.g., primary screening process (110))may have a simple criteria (e.g., maximizing current versus voltagemeasurements for a narrow wavelength band) to allow a quick evaluationand thereby quickly rule out materials that will not undergo the secondstage of testing (e.g., in secondary screening process ((120)) shown inFIG. 1). During the secondary screening process ((120)) shown in FIG. 1,a variety of more specific characterization methods may be performed onthe test cleaning formulations identified in primary screening process((110)) on fabricated patterned/metallized surfaces. Suchcharacterization methods include parametric tests and reliability tests.Sample criteria to evaluate include, but are not limited to: maximizingcurrent density, maximizing current versus voltage measurements, for anarrow wavelength band, and maximizing current versus voltagemeasurements for the bandwidth of sunlight.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of several embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of the appendedclaims.

1. An apparatus for measuring current-voltage (I-V) characteristics,said apparatus comprising: a lamp that emits light; a substratecomprising: a plurality of solar cells; a positive electrode operativelyconnected to each of the solar cells; and at least one negativeelectrode peripherally deposited around each of said solar cells andconnected to a common ground; an articulation platform operativelycoupled to said substrate and positioned at a fixed distance from saidlamp; a multi-probe switching matrix comprising a plurality of probes,wherein each probe is individually articulable; a programmable switchbox operatively coupled to said multi-probe switching matrix andselectively articulating said probes by raising said probes until saidprobes are in contact with at least one of said positive electrode andsaid negative electrode and lowering said probes until contact is lostwith at least one of said positive electrode and said negativeelectrode; and a source meter operatively coupled to said programmableswitch box and measuring said I-V characteristics of said substrate. 2.The apparatus of claim 1, wherein said lamp comprises a solar simulatorand said light comprises natural light with less than 1% difference ofsunlight.
 3. The apparatus of claim 1, further comprising a computingdevice operatively coupled to said programmable switch box, wherein saidcomputing device instructs said programmable switch box to articulate asingle positive electrode specific to a first solar cell and a singlenegative electrode specific to said first solar cell.
 4. The apparatusof claim 1, wherein said source meter comprises a multi-channel sourcemeter and each channel of said multi-channel source meter is coupled tosaid programmable switch box.
 5. The apparatus of claim 1, wherein eachprobe comprises a spring-loaded pin.
 6. The apparatus of claim 1,further comprising a pneumatic solenoid coupled to said multi-probeswitch matrix and said pneumatic solenoid articulates each probe using apneumatic pressure.
 7. The apparatus of claim 1, wherein each of saidsolar cells comprises a combinatorial variation of process conditions,said process conditions comprise at least one of texturing by wetchemistry and varied thin film deposition by dry processing.
 8. Theapparatus of claim 1, wherein said multi-probe switching matrixgeometrically matches said substrate.
 9. The apparatus of claim 1,wherein said articulation platform is actively cooled by air around saidarticulation platform.
 10. A current-voltage (I-V) characterization toolcomprising: a lamp that emits light; a substrate comprising: a pluralityof solar cells; a positive electrode centrally deposited in each of saidsolar cells; and at least one negative electrode peripherally depositedaround each of said solar cells and connected to a common ground; ashutter positioned between said lamp and said substrate, wherein saidshutter comprises an open position allowing said light to passingtherethrough to said substrate and a closed position blocking said lightfrom passing to said substrate; an X-Y stage tray operatively coupled tosaid substrate and positioned at a fixed distance from said shutter; amulti-axis control device operatively coupled to said X-Y stage tray,wherein said multi-axis control device articulates said X-Y stage trayalong a plane parallel to said X-Y stage tray; a Z-stage devicecomprising at least two probes, wherein said Z-stage device articulatesperpendicular to said X-Y stage tray; a source meter operatively coupledto said Z-stage device, wherein said source meter measures a currentfrom said substrate; and a computing device operatively coupled to saidZ-stage device, said shutter, and said X-Y stage tray, wherein saidcomputing device transmits first movement instructions to said Z-stagedevice and said X-Y stage tray thereby positioning a first site-isolatedregion of said substrate below said shutter as said shutter is in saidclosed position and further transmits second movement instructions tosaid shutter thereby moving said shutter into said opening position whensaid substrate is so positioned.
 11. The I-V characterization tool ofclaim 10, wherein each of said solar cells comprises a combinatorialvariation of process conditions, said process conditions comprise atleast one of texturing by wet chemistry and varied thin film depositionby dry processing.
 12. The I-V characterization tool of claim 10,further comprising clamp that secures said substrate to said X-Y stagetray.
 13. The I-V characterization tool of claim 10, further comprisingvacuum means for securing said substrate to said X-Y stage tray.
 14. TheI-V characterization tool of claim 10, wherein said articulating traycomprises: an X-axis articulator; an X-axis controller coupled to saidX-axis articulator; a Y-axis articulator; and a Y-axis controlleroperatively coupled to said X-axis controller and said Y-axisarticulator.
 15. The I-V characterization tool of claim 14, furthercomprising: a first remote controller operatively coupled to said X-axiscontroller and said computing device, wherein said first remotecontroller controls said X-axis controller in accordance with said firstmovement instructions received from said computing device; and a secondremote controller operatively coupled to said Y-axis controller and saidcomputing device, wherein said second remote controller controls saidY-axis controller in accordance with said first movement instructionsreceived from said computing device.
 16. The I-V characterization toolof claim 10, further comprising a pneumatic solenoid coupled to saidZ-stage device and said computing device, wherein said pneumaticsolenoid articulates said Z-stage device using pneumatic pressure uponreceiving said first movement instructions from said computing device.17. The I-V characterization tool of claim 10, wherein said probes aresufficiently spaced apart to permit each probe to have contact with atleast one of said positive electrode and said negative electrode whensaid Z-stage device is raised and said probes lose contact with at leastone of said positive electrode and said negative electrode when saidZ-stage device is lowered.
 18. The I-V characterization tool of claim10, wherein said X-Y stage tray is cooled by air around said X-Y stagetray.
 19. The I-V characterization tool of claim 10, wherein saidZ-stage device is operatively coupled to said X-Y stage tray, whereinsaid X-Y stage is operatively coupled to a support platform, and whereinsaid substrate is securely coupled to said support platform.
 20. Amethod of automating current-voltage (I-V) characterization measurementsof a substrate, said method comprising: receiving said a substrate,wherein said substrate comprises: a plurality of solar cells; a positiveelectrode contacting each of said solar cells; at least one negativeelectrode peripherally deposited around each of said solar cells andconnected to a common ground; and wherein each of said solar cells iscombinatorially varied; determining whether to use at least one of afrontside probing device and a backside probing device to probe saidsubstrate to measure for said I-V characterization measurements, whereinsaid determination is based on a type of said substrate; determining anumber of probes needed to test each of said solar cells of saidsubstrate; programming an I-V characterization tool to move at least oneprobe to contact at least one of said positive electrode and saidnegative electrode, wherein said I-V characterization tool comprises atleast one of said frontside probing device and said backside probingdevice; and determining said I-V characterization measurements for eachof said solar cells using said I-V characterization tool.